The official Vatican website was taken offline on Wednesday following an apparent hacking attack, the Holy See said.
"Technical investigations are ongoing due to abnormal attempts to access the site," Vatican spokesman Matteo Bruni said, without giving any further information.
The suspected hack came a day after Moscow criticised Pope Francis's latest condemnation of Russia's invasion of Ukraine.
In an interview with a Jesuit magazine, the pope had singled out troops from Chechnya and other ethnic minorities in Russia for their particular "cruelty" during the war.
Earlier this week, the Kremlin said it would support mediation from the pope, but that leaders in Ukraine had made it impossible.
The pontiff has offered to host negotiations multiple times, including last week.
He also said Ukrianians were a 'martyred people'.
The source of the attack has not come forward.
The Vatican website has been attacked multiple times, by multiple groups. Anonymous - an activist group known for infiltrating online systems - one bombarded the Holy See website with traffic, rendering it unusable.
It's also believed Chinese hackers gained access in 2020.
(Additional reporting by Reuters)